Abstract
The development of targeted therapies requires the identification of specific sites to which molecular ligands can selectively bind with high affinity. Dendrimers offer an excellent platform for designing, synthesizing, and evaluating theranostic approaches due to their multifunctional features useful for multimodal imaging and for providing more than one therapeutic option.
Dendrimers have been studied for biomedical applications, including imaging or treating infections, neurological disorders, and cardiovascular and oncological diseases. Dendritic macromolecules have also been designed to interact with nucleic acids to produce gene therapy. Dendrimer-based theranostic agents also include radiolabeled dendrimers as smart platforms to deliver radiation doses and cytotoxic cargos at a specific target within the cell.
This chapter will provide a brief overview of the progress made in the design and development of dendrimers used for therapy and imaging over the last decade, focused on preclinical evaluation and the exploration of the potential of these nanoapproaches to be translated into the clinical practice.
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1 Introduction
Dendrimers are considered as novel drug delivery systems. For the last 15 years, this type of branched architectural nanosystems has been studied and mainly focuses on design parameters such as shape, architecture, size, elemental composition, surface chemistry, and flexibility [1]. Dendrimers have been proposed as a platform for vaccines, for delivering drugs or genes.
In the field of therapeutics, these three-dimensional polymers have demonstrated potential as intratumoral or intracellular delivery vectors. They have also been widely studied as targeted and controlled systems for delivering anticancer agents, nucleic acids, or antiviral drugs. Drugs encapsulated in dendrimers include anti-inflammatory, antiviral, nonsteroidal, or antimicrobial compounds. The most studied dendrimers are poly(amidoamine) (PAMAM) and poly(propylene imine) (PPI)-based.
In dendrimer chemistry, click and orthogonal chemistries have been useful tools for their synthesis. Although dendrimers have been used to contain drugs inside, many approaches fail to fulfill their specific function or their response is very limited since only part of them reaches the site of interest. Effective targeted drug delivery systems require the following properties: drug retention, immune system evasion, specific targeting, and selective cargo release. The most explored application of dendrimers is targeted cancer therapy, particularly in the use of combined therapies, where dendrimers’ multifunctional properties can potentially improve therapeutic responses [2].
Dendrimer-based nanoapproaches are also promising for clinical translation. However, enabling them more functionalities implies more challenges for their chemical and/or biological characterization.
Since dendrimers exemplify one of the most studied scaffolds for anticancer drugs, this chapter focuses on reviewing dendrimer-based systems developed for modalities that combine controlled and sustained drug or gene delivery for biomedical applications in anticancer therapies.
2 Chemical Properties
Dendrimers are highly branched three-dimensional polymers, similar to a tree arrangement. These are monodispersed, with nanometric size (1–100 nm) and well-defined structure and molecular weight [3]. The general architecture of dendrimers (Fig. 1) shows three main components: (a) inner core, composed of a central atom or group of atoms, (b) inner layers, consisting of repeating branching units, and (c) multiple external moieties attached to the branches, which play a determining role in their physicochemical and biological properties. Their shape, size, and surface charge can be modified by the chemical nature and level of the repeating units.
Schematic representation of dendrimers
The functional entity of the dendrimer is called “dendron” and multiple molecules can be attached to their surface or trapped on its branches.
As the size of the dendrimers increases, they adopt a spheroidal structure to minimize repulsion between their branches. The dendrimer properties differ from their linear analog and are influenced by the exterior functional group. The superficial groups can be selected or modified to impart distinct characteristics to the dendrimer structure, such as solubility, lipophilic or hydrophilic properties, miscibility, and acidity [4].
In general, there are two main strategies for dendrimer synthesis: divergent and convergent. The synthesis in the divergent method begins from the central core to the periphery. This growth process starts with nucleus activation and the first monomeric unit linkage; subsequently, growth depends on the repetition of two essential steps, namely, (a) activation of the monomer end group and (b) coupling of new monomers, until the acquisition of the desired dendrimer. The addition of a new generation of branches requires that each step of the reaction be fully completed allowing the synthesis of highly symmetric dendrimer molecules. This method is not a limitation to search for dendrimers with different types of peripheral groups. The divergent process allows symmetric internal branches but is possible to incorporate heterogeneous terminal monomers for better applications [5, 6].
On the other hand, the convergent approach does not start from the core but from what will make up the external structure of the dendrimer. It also requires repetitive steps of activation and incorporation of new structures. The growth process starts when the peripheral groups bind a monomer unit. Posteriorly, this fragment is activated and the reaction with other monomers is promoted to produce the initial dendron. The activation reaction and monomer addition can be repeated until reaching specific dendrons and, finally, coupling with the inner core, to provide the expected dendrimer structure [6].
Compared to the divergent method, the convergent method yields dendrimers of higher purity due to fewer coupling reactions at each growth step. However, steric hindrance makes it difficult for the dendrimer arms to react with the inner core. Synthesis of symmetric and asymmetric dendrimers is possible because of the capability of controlling the addition of homogeneous or heterogeneous dendrons, providing several active sites and versatile dendrimers for different applications.
In both methods, specific and successive reaction steps allow the incorporation of new branches, and the number of repeated steps or a new level of branches is called dendrimer generation (G). Normally, the first dendrimer-core activation and modification is called generation 0, and there are intermediate generations, beginning with G0.5, until achieving the most common generations, such as G1 to G10.
An increase in G produces an increase in dendrimer volume and confers greater density and the number of terminal groups. For example, lower-generation dendrimers possess more open structures and, occasionally, an asymmetric shape. However, as the dendrimer generation increases, the dendrimers become globular and densely packed structures. When hyperbranching becomes critical, dendrimers cannot grow uniformly because of steric impediments.
The physicochemical properties such as solubility, miscibility, glass transition temperature, and chemical reactivity are mainly influenced by the features of the peripheral chemical motifs and not by their core or branches. Dendrimer solubility also varies with the change of superficial groups. Hydrophilic superficial groups allow high solubility in polar solvents, whereas the hydrophobic groups are responsible for the solubility in nonpolar solvents. Additionally, dendrimers show some improved physicochemical properties compared to analogous linear polymers. For example, dendrimer solutions have a lower viscosity than the corresponding linear polymer [6].
Dendrimers exhibit cytotoxicity dependent on generation, charge, and concentration. In general, toxicity increases in high generations, and cationic structures exhibit high toxicity levels compared to neutral or anionic dendrimers. To reduce the toxicity levels, the selection of neutral or anionic biocompatible dendrimers and their surface modification with more biocompatible groups have been explored [7].
Therefore, the specific control over dendrimer architectures, such as shape, the presence of internal cavities, and specific peripheral groups, makes dendrimers an ideal pharmaceutical per se, or as ideal carriers of drugs, metals, and imaging moieties, among others, for biomedical application [6, 8]. Dendrimers can load and store diverse molecules by encapsulation of molecules into their cavities, absorption on the surface by electrostatic interactions, or conjugation (through covalent bonding) with the surface groups (Fig. 2).
Representation of possible ways of loading molecules in the dendrimer. (a) encapsulation in internal cavities, (b) electrostatic interactions, and (c) covalent bonding
Among the most-studied dendrimer families, there are the poly(amidoamine) (PAMAM, the first synthesized dendrimers), poly(propylene imine) (PPI), polyether-copolyester (PEPE), poly-L-lysine (PLL), polyester, triazine, polyether, citric acid, phosphorous, peptide dendrimers, and PEGylated dendrimers, which garner a wide interest for their innumerable potential applications in the medical field [9].
3 Biological Properties and Uptake Mechanisms
Dendrimers have proven to be molecules with good biocompatibility that can be used as therapeutic agent carriers so that they represent promising vectors for different biological and pharmaceutical applications. Thus, the dendrimers must be nontoxic and must not activate the immune system [10].
3.1 Cytotoxicity
The factors that determine the cytotoxicity of dendrimers depend on their generation, charge, and type of functional groups on their exterior. Toxicity levels increase as dendrimer along with the generation. The amine type and substitution level give them different peripheral charges (positive, negative, or neutral charges) that interact differently with the biological membrane. Positively charged dendrimers show higher toxicity when compared with that neutral or anionic dendrimers, and this is because the positive charges interact with the lipid bilayer, weakening membrane integrity, and increased permeability, with the consequent cell lysis. Different studies have shown that dendrimers possessing surface amine groups such as PAMAM and PPI are characterized by higher toxicity (generation- and concentration-dependent) in contrast with grafted carbosilane-poly(ethylene oxide) dendrimers and other dendrimers with anionic or neutral surface groups [9, 10]. PAMAM dendrimers with amino groups on the surface have lower cytotoxicity compared to the linear amino-terminated polymer, causing hemolysis, due to the cationic superficial groups on the PAMAM [10, 11]. Similar to PAMAM with amino-terminal groups, PPI dendrimers show hemolytic effects and generation-dependent cytotoxicity [12].
One way to improve dendrimers’ biocompatibility and reduce toxicity is through surface modification of the conjugated dendrimer with functional moieties such as targeting ligands, imaging agents, drugs, and radionuclides. Generally, PAMAM, PPI, and PEI (polyethyleneimine) dendrimers possess modified positively charged groups on their surface with anionic or neutral residues to reduce their toxicity and hepatic accumulation. This is why PAMAM dendrimers show differences in toxicity when functionalized with hydrophobic end groups, polyethylene glycol (PEG), OH, and pyrrolidine [13, 14].
3.2 Cellular Internalization and Action on the Mononuclear Phagocyte System
Like cytotoxicity, dendrimer cellular uptake mechanisms vary considerably due to generation, functionalization, surface charge, concentration, and cell type. Dendrimers can pass through the cell membrane via an energy-independent process, but the main internalization mechanism is endocytosis, an energy-dependent process [13, 14]. There are different endocytosis mechanisms; the main is shown in Fig. 3.
Endocytosis mechanisms. Macropinocytosis, clathrin-mediated endocytosis (CME), and caveolin-mediated endocytosis (CVME) are the main receptor-mediated endocytosis (RME) mechanisms
Phagocytosis is the uptake of particulate with a size range of micrometer by vesicles inside the cell, and it is a mechanism rarely used by dendrimers. Pinocytosis consists of the uptake of fluids by vesicles smaller than those present in phagocytosis. This internalization mechanism is classified into macropinocytosis and receptor-mediated endocytosis.
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Macropinocytosis involves the uptake by vacuoles called macropinosomes. After the internalization of macropinosomes, there is a decrease in pH, and endosomal markers appear. Finally, macropinosomes can fuse with late endosomes, with lysosomes, or recycle their cargo to the membrane [15].
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Receptor-mediated endocytosis, the most frequent pathway for nanoparticle internalization, can be through the following:
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Clathrin-mediated endocytosis (CME) occurs in regions where clathrin is recruited in the plasma membrane. First, clathrin-coated endocytic vesicles (70–150 nm) are formed, as a response to the interaction of an agonist with its receptor. Then, the internalized vesicle loses its clathrin coat and fuses with other vesicles to form an early endosome, which becomes a late endosome that eventually fuses with a lysosome [16].
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Caveolin-mediated endocytosis consists of invaginations (60–80 nm) of the plasma membrane, which incorporate extracellular fluid content. Proteins like caveolin-1 bind to cholesterol in lipid rafts, which do not dissociate from the vesicles after uptake. Caveolin vesicles are formed and fused with other caveolin vesicles, giving rise to multicaveolar structures called caveosomes, which fuse with early endosomes [17].
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The pathway by which dendrimers enter the cell is broad and dependent on the type of cell and dendrimer. Concerning size, dendrimer internalization is greater in nonphagocytic cells with a size around 50 nm, while for a size between 150 and up to 200 nm, internalization has been observed mainly through CME or CVME, and above 250 nm and up to 3 μm showed better in vitro uptake through phagocytosis and macropinocytosis [18].
Regarding the generation of PAMAM dendrimers, it has been reported that dendrimers higher than the fourth generation show the highest internalization rate, due to their ability to form pores and eliminate lipids from the membranes, while dendrimers <G-5 are intercalated or adsorbed onto the membrane surface. The charge has also a large impact, as this behavior is governed by electrostatic interactions between charged dendrimeric structures and the lipidic membranes, which give rise to greater membrane disruption compared to uncharged dendrimers [13, 14].
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Chemical modification can influence the uptake pathway. Authors have reported that amino-ended PAMAM dendrimers (cationic) stimulate effective cellular uptake by endocytosis and through membrane pore formation [13, 14, 17, 19] (Table 1).
4 Dendrimers for Imaging
Molecular imaging has provided the opportunity for obtaining high-resolution physiological information. Molecular imaging modalities comprise positron emission tomography (PET), single-photon emission computed tomography (SPECT), optical tomography imaging, computed tomography (CT), and magnetic resonance imaging (MRI) [26].
Molecular images are acquired from fluorescent molecules, γ-emitting radionuclides, or metal oxides. Radiolabeled imaging probes allow their noninvasive in vivo biodistribution and pharmacokinetics monitoring by the PET or SPECT nuclear modalities [27]. Dendrimers can be radiolabeled with diagnostic, therapeutic, or theranostic isotopes through several strategies, for example, using bifunctional chelating agents [28]. Technetium-99 m (99mTc) and Indium-111 (111In) are the most common SPECT radionuclides employed for this aim, while for PET applications, Gallium-68 (68Ga) and Copper-64 (64Cu) are the most-studied radionuclides [29].
4.1 Dendrimers for PET Imaging
Targeted dendrimers have been synthesized and successfully labeled with 64Cu to obtain PET images of tumors overexpressing receptors (Fig. 4). G5 PAMAM dendrimers conjugated to folic acid (FA) and labeled with 64Cu-DOTA show specific recognition of cancer cells and tumor xenografts that overexpress folate receptors. Since the DOTA chelator is suitable for radioactive labeling with other radiometals, these dendrimers can also be employed for SPECT nuclear imaging and radiotherapy with yttrium-90 or lutetium-177 [30]. Furthermore, dendrimers can penetrate the tumor via the enhanced permeability and retention (EPR) effect, due to dysfunctional vascularization and lymphatic drainage in the tumors. The EPR also called the “passive effect of the tumor target” enables the imaging agent for increasing its concentration in the tumor, improving in this way the resolution and sensitivity of the image [31]. Another example of an imaging system based on dendrimers is the triazine dendrimer functionalized with DOTA, which presents the characteristic of reacting with the urea-based ligand (DUPA). DUPA has an affinity for the prostate-specific membrane antigen (PSMA). Targeted uptake of 64Cu-labeled dendrimers, G1-(DUPA)64 and G5-(DUPA)64, was systematically assessed using positive PSMA PC3-PIP and negative PSMA PC3-FLU cell lines. From these studies, the G1-(DUPA)64 showed the highest uptake for PC3-PIP, while G5-(DUPA)64 exhibited the highest affinity for PSMA. PET studies showed that nontargeted uptake increased as a function of the size, despite the good multivalence of larger dendrimers [32].
Examples of dendrimer-based nanosystems for imaging. (a) G5 PAMAM dendrimers conjugated to folic acid (FA) and labeled with 64Cu-DOTA for PET imaging. (b) G5 PAMAM dendrimers, terminated by an amine (G5 NH2) modified with 3-(4′ hydroxyphenyl)propionic-OSu acid (HPAO) and FA, coupled to PEG, modified by acetylation of the remaining dendrimer surface amines and labeled with radioactive iodine-131 for SPECT. (c) Folate receptor (FR)-targeted dendrimer, PEG-G3-(gadolinium-DTPA)11-(folate)5 for magnetic resonance imaging
4.2 Dendrimers for SPECT Imaging
To acquire SPECT images, G5 PAMAM dendrimers, terminated by an amine (G5 NH2), have been modified using 3-(4′-hydroxyphenyl)propionic-OSu acid and folic acid (FA), coupled to polyethyleneglycol. Additionally, these dendrimers were modified through acetylation of the remaining surface amine motifs and radiolabeled with iodine-131 (131I). Multifunctional NHAc-HPAO-PEG-FA G-5 dendrimers radiolabeled with 131I were also reported as effective approaches for targeted SPECT imaging and concomitant therapy of a xenograft tumor model overexpressing folate receptors [33]. In addition to being excellent platforms for SPECT images, dendrimers are also used for SPECT-CT imaging applied to post-chemotherapy evaluation on cancer cell apoptosis. These platforms are PAMAM dendrimers (G-5) loaded with gold nanoparticles, conjugated to DOTA, PEG-duramycin, fluorescein isothiocyanate, and radiolabeled with 99mTc. In vivo micro-CT imaging data indicates that these dendrimers can be used to obtain specific CT images of the premature tumor reaction to treatment [34]. The 99mTc-PAMAM-Tyr3-Octreotide multimeric nanosystem was designed for neuroendocrine tumor imaging. The [Tyr3-Lys(Boc)5]-octreotide was conjugated to the –COO− motifs on the surface of PAMAM dendrimer (G3.5). The radioactivity distribution on tissue 2 h after 99mTc-PAMAM-Tyr3-Octreotide administration showed specific tumor uptake of 4.12 ± 0.57%ID/g and high pancreas uptake which overexpresses high density of somatostatin receptors. The dendrimer peptide displayed suitable features to be used as a target imaging agent for tumors overexpressing somatostatin receptors [35].
4.3 Dendrimers for CT Imaging
Dendrimers are an essential and stable nanoparticle system for developing contrast agents for X-ray medical imaging [36]. Gold nanoparticles, encapsulated in dendrimers, are an example of contrast agents since gold nanoparticles exhibit high X-ray attenuation in comparison with conventional contrast agents based on molecular iodine [37]. For improvement of CT imaging, dendrimers with gold nanoparticles and conjugated to an iodinated small molecule can be prepared. These two radio-dense gold and iodine components enhance the sensitivity of CT images [38]. Moreover, to provide specificity to contrast agents based on nanoparticles, ligands (e.g., FA, Arg-Gly-Asp (RGD) sequence, and lactobionic acid) can bind covalently to a dendrimeric structure. For example, FA has been bound to the surface of dendrimers, with entrapped gold nanoparticles, through a 1-ethyl-3-(3-dimethylaminepropyl) carbodiimide hydrochloride coupling reaction for CT imaging of human cancers that overexpress folate receptor [39]. Moreover, for dual CT and magnetic resonance imaging (MRI) multifunctional tecto dendrimers, encapsulating gold nanoparticles, have been designed. Gold nanoparticles are encapsulated in β-cyclodextrin-modified G5 PAMAM dendrimers to obtain a dual probe. Dendrimers were sequentially modified with RGD peptide via a PEG spacer, gadolinium chelator, and 1,2-propane sultone, followed by chelation of Gd (III) ions. These dual systems, based on dendrimers, show suitable colloidal stability, high X-ray attenuation, relaxivity, suitable anti-fouling properties, and good cytocompatibility. In addition, these nanoparticles target cancer cells that overexpress the integrin αvβ3, due to their functionalization with RGD [40].
4.4 Dendrimers for Magnetic Resonance Imaging
Dendrimers have been shown to significantly affect magnetic resonance relaxivities and physiological properties of magnetic nanoparticles. Therefore, dendrimer magnetic nanoparticle agents are desired to supply sharper images with physiologically relevant contrast, longer retention times in blood, and specific organ uptake. Fine-tuning the size and functionalities of the final group of dendrimers supply an additional advantage in this regard (Fig. 4) [41]. For developed injectable contrast agents in MRI, dendrimers have been used to incorporate gadolinium chelates, including paramagnetic iron oxide particles (magneto-dendrimers), to label and track cells [42]. Dendrimers act as a central platform for the transport of small molecules such as Gd ions or Gd (III) chelates for magnetic resonance contrast. Such molecules must be on the dendrimer surface to allow them to interact freely with water molecules. PEGylated dendrimers exhibit a much higher Gd(III) concentration in blood than other dendrimer formulations [43]. These dendrimers have been modified with folate or antibodies, poly-L-lysine, and PEG to improve the in vivo circulation time [42,43,44].
5 Targeted Drug Delivery Based on Dendrimers
Although dendrimers have been used to transport drugs, to increase their bioavailability and their active fraction, it has been shown that functionalization with biomolecules is the best strategy to improve the delivery to the tissues of interest. Dendrimers without functionalization are likely to be insufficient to produce significant clinical benefits. Therefore, special emphasis has been directed toward delivering cytotoxic drugs used as chemotherapeutic agents for cancer treatment [2]. Targeted drug delivery involves the transport of a therapeutic agent to a specific tissue without affecting healthy tissues in the body.
Effective targeted drug delivery systems need to be retained, evade healthy organs or tissues, target specific tissues, and be released in the selected regions [2]. The most-explored use of dendrimers is the targeted therapy of cancers. Besides, dendrimers have the capability of being grafted with two or more targeting biomolecules to enhance selectivity.
The targeted delivery of therapeutic agents can be systemic, through blood circulation and extravasation (ligand-receptor mediated), or intracellular (by self-triggered cargo delivery) [2]. Regarding the size of nanoparticles, their accumulation occurs faster when compared to larger molecules; larger molecules are retained longer inside the tumor but can also be diffused back into the systemic vascular bed.
Active targeting is generally achieved through biomolecules which improve the accumulation in cancer cells, and intracellular organelles, within the tumor or a tumor-bearing organ [45]. Retention, evasion, targeting, and release features should be considered when designing effective targeted drug delivery nanosystems [46].
Targeting cell-surface receptors enable nanoparticles to be internalized at the cell surface or into the microenvironment. When nanoparticles are decorated with tumor-targeting biomolecules, these nanoparticles can target cancer-specific receptors or the tumor microenvironment with great specificity. In this context, several approaches have shown synergistic effects when targeted drug delivery systems, based on dendrimers, are used. The drug inside dendrimers can be achieved through encapsulation or conjugation of drugs by covalent bonds. Drugs encapsulated in dendrimers include nonsteroidal anti-inflammatory drugs and antiviral or antimicrobial compounds; however, the most-explored targeted drug delivery systems are for anticancer therapy. Several receptors are overexpressed in cancer. Therefore, anticancer drugs can be concentrated in target sites by encapsulation or conjugation of drugs to the dendrimer surface with biomolecules that possess affinity toward these receptors.
Different types of targeting biomolecules, such as RGD, FA, aptamers, and other biomolecules, have been used to functionalize dendrimers encapsulating or bound to cytotoxic agents, against several cancer types.
The camptothecin SN38 (7-ethyl-10-hydroxy-camptothecin), a replication and transcription inhibitor, was encapsulated in PAMAM dendrimers functionalized with BR2 and CyLoP1 cell-penetrating peptides. A family of synthesized derivatives was evaluated and demonstrated a significant tumor growth inhibition when they were compared against their commercial counterparts, on colon carcinoma cells [47].
For colon cancer, PAMAM dendrimers were functionalized to target laminin receptors through the YIGSR sequence peptide, and gemcitabine was encapsulated within these [48]. After exposure to treatment, the targeted nanoapproach was internalized to the cytoplasm and the nucleus of the HCT-116 cell line. The gemcitabine-loaded dendrimer showed greater mortality at 24 h when compared to normal fibroblasts.
Also, natural compounds like curcumin have been encapsulated within dendrimer structures to provide mitochondrial anticancer therapy for hepatocellular carcinoma through TPP (triphenylphosphonium) to target the mitochondria [49]. In this specific case, the curcumin and TPP were conjugated to the PAMAM structure. As a result, selective toxicity against cancer cells was observed.
5.1 Folate Receptors
The presence of FA on the dendrimer surface has demonstrated improvement of the specific therapeutic response. FA has been attached to PPI dendrimers, as carriers for methotrexate (MTX). The MTX was covalently bound to the dendrimer surface, by EDC activation, and in vitro and in vivo characterization was carried out [50].
Doxorubicin has been conjugated to PAMAM dendrimers (G.5) and functionalized with FA. The nanosystem was conjugated to fluorescein isothiocyanate for fluorescence microscopic imaging. This approach did not exhibit important toxicity. The NAHAc-FI-FA-DOX (G-5) demonstrated stability and showed a sustained-release profile. The nanosystem specifically targets folate receptors on KB cells, with the consequent high toxicity toward this cell line [51]. Recent nanoapproaches based on triazine dendrimers grafted with a photoluminescent FA derivative, which showed a pH-dependent DOX release, were proposed as a suitable photoluminescent nanoapproach antineoplastic drug delivery [52]. The stability of FA dendrimers G3 and G4 was increased along with the size, and the loading efficacy was higher for doxorubicin when compared to tetracycline and tamoxifen [53].
Also, to monitor cells positive for folate receptors via imaging techniques, radionuclides have been attached too. These nanoapproaches will be studied in the “Imaging” section.
MTX has been encapsulated by or conjugated to PPI dendrimers targeted at folate receptors and evaluated at the preclinical stage in the MCF-7 breast cancer cell line [50].
Some reports have demonstrated that PEG formulations also exhibit enhanced responses against cancer cells when loaded with 5-fluoroacyl (5-FU) [54]; FA-conjugated PEG dendrimers loaded with 5-FU (31% encapsulation) showed important uptake with a sustained drug release profile and high uptake when compared to a non-PEGylated approach [55]. 99mTc was bound to PEG-PAMAM-FA, loaded with 5-FU, to provide specific therapy on MDA-MB-231 cells [56].
Molecular dynamics simulations have demonstrated that increasing the degree of PEGylation produces an improvement over the total 5-fluoroacyl loading capacity, while a 25% PEGylated system was proposed as the best choice for drug delivery procedures [46]. In the case of MTX release, the simulations suggest that a high PEGylation ratio limits MTX diffusion toward inner cavities, with the consequent decrease of MTX release [57].
5.2 Epidermal Growth Factor Receptor (EGFR)
To target EGFR, the specific sequence peptide ARSHVGYTGAR was conjugated to poly-lysine dendritic nanoplatforms, to deliver MTX for preclinical evaluation. The preliminary studies showed a suitable in vivo therapeutic efficacy [54]. EBP-1 (EGFR-binding peptide 1) was also used to functionalize PAMAM dendrimers loaded with DOX, which improved the antiproliferation effect of DOX in breast cancer cells [58]. Gefitinib and hematoporphyrin were encapsulated within a fluorinated dendrimer functionalized with an aptamer, to recognize EGFR-positive cells in non-small cell lung cancer [59].
5.3 Integrin Receptors
Integrin receptors overexpressed in neovasculature have also been targeted via RGD-functionalized PAMAM G-5 dendrimers and modified with fluorescein isothiocyanate and PEG, which were loaded with approximately six molecules of DOX each [60, 61].
Chemotherapy in gliomas represents a big challenge due to the low penetration through the blood-brain and blood-tumor barriers. Thus, a PEGylated PAMAM dendrimer (G-5) was loaded with arsenic trioxide (As2O3, ATO) to produce RGDyC-mPEG-PAMAM/ATO, as a promising nanosystem for the treatment of gliomas. Results showed specific targeted drug delivery, with long circulation time and an improved antitumor efficacy (by RGD), when compared to As2O3 alone [62].
A recent study demonstrated that functionalization with RGD improves the internalization of the synthesized nanosystem in resistant cells, allowing the efficient delivery of paclitaxel within KB CHR8–5 cells, thus improving apoptotic mechanisms [63].
Another kind of therapy incorporates targeted radio- or photodynamic therapy, for example, by using PAMAM-DOTA-cRGDfK, which was prepared and radiolabeled with lutetium-177, to produce targeted integrin αvβ3 radiotherapy [64]. Multiple chorine e6 molecules were covalently bound to a PAMAM dendrimer (G-7) to produce specific cell death in cells positive for integrins, at nanomolar concentrations, under photo-irradiation [65].
5.4 CXCR4 Receptors
CXCR4 is a chemokine receptor involved in the progression and metastatic process of cancers. They are highly expressed in several cancer types [9, 10]. The efficacy of dendrimers functionalized with the LFC131 (Tyr-Arg-Arg-Nal-Gly) peptide sequence, covalently bound and loaded with DOX, significantly improved binding when compared to dendrimer-DOX (without targeting moiety) and presented enhanced cytotoxicity, with regard to BT-549-Luc and T47D, attributed to the binding of the LFC131 peptide to the CXCR4 receptor [55].
5.5 Somatostatin Receptors
PAMAM dendrimers have also been designed and synthesized for somatostatin receptor binding and MTX delivery in MCF7 cells and demonstrated enhanced cytotoxicity when compared to free MTX [56].
6 Dendrimers for Gene Therapies
Gene therapy is an emerging therapeutic strategy that consists in modifying the target gene expression through nucleic acids release into the cell, such as antisense oligonucleotides (AO), small interfering RNA (siRNA), microRNA (miRNA), or short hairpin RNA (shRNA) [66,67,68]. These nucleic acids present diverse modes of action to achieve their therapeutic effect (Table 2).
The nucleic acids can be ex vivo or in vivo delivered to the target cell. In the ex vivo method, the stem cells removed from the patient are transfected with the therapeutic gene in vitro. The genetically modified cells are introduced into the patient, where the stem cells can differentiate and the gene can be expressed. In contrast, with the in vivo method, a therapeutic gene is directly administered to the patient via systemic or localized injection [79, 80]. The latter is less efficient in reaching the target site, due to multiple factors, such as enzymatic degradation, immune activation, undesired protein interactions, and limited cellular uptake [80, 81]. To counteract and increase the probability of delivery of the genetic material into the target cell, different transport systems, based on organic nanoparticles, have been evaluated [67, 70, 81,82,83,84,85,86,87,88]. Dendrimers represent an efficient nucleic acid delivery strategy (Fig. 5). PAMAM dendrimers are currently the most studied. These dendrimers form stable complexes with RNA or DNA employing electrostatic interactions, giving rise to dendriplexes [83, 89]. Dendrimers also protect nucleic acids from enzymatic degradation and facilitate endosomal escape [87, 88]. Endosomal escape occurs when tertiary amines in dendrimer structures get protonated within endosomes. This induces the flux of negatively charged ions (Cl−), which disrupts the endosome membrane, with the consequent release of nucleic acids [88]. Pedziwiatr-Werbicka et al. (2011) mention that the nature of the dendriplexes depends on the concentration and stoichiometry of the DNA phosphates and dendrimer-amines, as well as on the solvent properties (salt concentration, pH, buffer strength) and even the dynamics of the mixing process [90]. The dendrimers’ clinical applications are still restricted, due to their biocompatibility and cytotoxicity. To counteract the above, chemical modifications on the surface or in the core of the dendrimers have led to the development of dendriplexes with a greater capacity to transport and release nucleic acids into target cells. Particularly, PAMAM, PPI, PLL, phosphoric, and carbosilane dendrimers are the most-used cationic dendrimers for the release of DNA or RNA [87].
Schematic representation of several nucleic acids transported by dendrimers
Since amine-ended PAMAM is positively charged at physiological pH, complex formation with nucleic acids is favored [89, 91]. There is evidence that PAMAM transfection efficiency increases with the increase in dendrimer generation [87]. Low-generation PAMAM dendrimers, such as G1 and/or G2 dendrimers, have few primary surface amines (i.e., low positively charge density), which limits nucleic acid complexation and transfection [88, 92]. The most efficient transfection is seen with intermediate and high PAMAM generations, including G3–G10, which is associated with the high density of surface primary amines [88, 89, 92]. However, these dendrimers have more rigid structures and are highly toxic. PAMAM toxicity is related to nanohole formation in cell membranes, by the effect of the interaction with positively charged primary amines [88, 89]. Chemical modifications of PAMAM dendrimer surfaces and core are a strategy for reducing cytotoxicity and promoting gene delivery [87, 92,93,94,95].
The partial acetylation or PEGylation of the surface groups is recommended to increase the biocompatibility of PAMAM dendrimers [89, 96, 97]. As a result of these reactions, a charge density reduction is produced. Fant et al. (2010) found that acetylation and PEGylation of G4 and G5 PAMAM dendrimers reduce cytotoxicity. However, the transfection efficiency is lower than that of the nonmodified dendrimer [89]. Shakbazau et al. (2010) proposed that decrease in transfection efficiency in acetylated G4 dendrimers is due to an increase in hydrophobicity [97]. Froehlkish (2011) examined DNA interactions with mPEG-PAMAM (G-3), mPEG-PAMAM (G-4), and PAMAM (G-4), keeping DNA concentration constant. The structural analysis demonstrated a strong dendrimer-DNA interaction via major and minor grooves and the backbone phosphate group with binding constants of KmPEG (G-3) = 1.5 ± 0.5 × 103 M−1, KmPEG (G-4) = 3.4 ± 0.8 × 103 M−1, and KmPAMAM (G-4) = 8.2 ± 0.9 × 103 M−1. The reported dendrimer-DNA complexation stability was PAMAM (G-4) > mPEG (G-4) > mPEG (G-3); this effect was associated with the neutralization of charges [98].
The conjugation of bromoalkylcarboxylates (of different chain lengths) with different percentages of primary amines of dendrimers is another strategy that has been used for the modification of the drug delivery efficiency in terms of drug solubility, release profile, and cytotoxicity [99, 100]. Alkylated PAMAM dendrimers were synthesized for targeted siRNA release to lung blood vessels, to treat chronic asthma and obstructive pulmonary disease. Using a combinatorial approach, the free amines on PAMAM dendrimers (of increasing generations) were substituted for alkyl epoxides of various carbon chain lengths. Such modifications improved the avidity of dendrimers for Tier2-positive endothelial cells in the lung [100].
Studies have shown that peptide functionalization in PAMAM dendrimers improves cell-penetrating ability, useful for targeted gene delivery. For example, a siRNA delivery system, based on a G4 PAMAM dendrimer, was conjugated to cell-penetrating peptides, oligo-arginine, and a transactivator of transcription, through a PEG crosslinker. The siRNA in this dendrimer carried out effective gene silencing of AT1R in cardiomyocytes [101].
Arima et al. (2011) prepared siRNA complexes employing a G3 PAMAM conjugate loaded with α-cyclodextrin and studied the intracellular distribution and in vitro RNAi effects on endogenous gene expression. Cyclodextrins interact with cholesterol and phospholipids of the cell membrane, resulting in augmented membrane permeability of hydrophilic compounds (i.e., siRNA). The dendrimer delivered fluorophore-labeled siRNA only into the cytoplasm and showed the efficient gene silencing of Lamin A/C and Fas expression after transfection [102]. Recently, Hersh et al. (2021) modified a G5 PAMAM dendrimer-DNA complex with a skeletal muscle-targeting peptide, a DLC8-binding peptide for enhancement of intracellular transport, and a nuclear localization signaling peptide for nuclear uptake complexed to plasmid DNA (containing the microdystrophin gene). This nanocarrier was able to induce microdystrophin protein expression, with the potential to be a therapeutic agent for Duchenne muscular dystrophy [83].
To obtain more flexible dendriplexes, some PAMAM dendrimers have been designed with an ethylenediamine [87] or triethanolamine (TEA) core [103]. The branching units in TEA core-based dendrimers are characterized by being less-densely packed, allowing optimal interaction with siRNA and increasing release properties. The TEA core can effectively protect siRNA from degradation and facilitate cellular uptake of siRNA via micropinocytosis [103].
Several strategies to inhibit the expression of target genes, at the mRNA level, have become popular recently. For example, mRNA or pre-mRNA containing specific nucleotide sequences allows the design of antisense oligonucleotides specific to target genes [69]. The first in vivo applications of AO showed limited clinical potential because of unfavorable properties such as rapid degradation by nucleases, poor uptake through cell membranes, and suboptimal binding affinity for complementary sequences [72, 81, 104]. Such characteristics increased the possibilities for using dendrimers as nanocarriers for therapeutic antisense oligonucleotides. Table 3 shows some examples of PAMAM dendrimers for the delivery of antisense oligonucleotides.
PPI dendrimers, composed of a 1,4-diaminobutane nucleus and branching units of propylene imine monomers, comprise only tertiary amine groups in the inner structure and primary amines on the surface. Ethylenediamine and other molecules can also be used as a dendrimer core [95, 112, 113]. The presence of alkyl chains in their branching units provides a more hydrophobic interior compared to PAMAM dendrimers [112]. Similar to PAMAM dendrimers, chemical modifications on the surface of PPI have been carried out to reduce toxicity and increase colloidal stability and uptake by target cells. The addition of hydrophobic moieties and/or cross-linker fragments containing dithiol, followed by PEG coating of PPI dendrimers, has led to enhanced DNA or RNA transfection [95, 112]. For example, Hashemi et al. (2015) evaluated the effect of the conjugation of bromoalkanoic acids with different side chains lengths (6, 10, and 16 carbons) and three different substitution degrees of substitution (10%, 30%, and 50% of surface amines) onto G5 PPI dendrimers, for DNA transfection. The hydrophobic modifications improved transfection activity, exhibiting higher DNA delivery for 30% and 50% grafting with decanoate moieties when compared to native G5 PPI [112]. For targeted dendriplexes, tyrosine modification of PPI shows high efficacy of gene knockdown with regard to EGFP activity mediated by siRNA [94]. Jugel et al. (2021) have reported the targeted delivery of a therapeutic siRNA specific for BIRC5/Survivin in tumor cells expressing the prostate stem cell antigen (PSCA). The single-chain antibody fragments (specific for PSCA) were conjugated to siRNA/maltose-modified PPI dendriplexes; these targeted polyplexes induced the knockdown of firefly luciferase and Survivin expression in prostate cancer cells and PC3/PSCA xenograft-bearing mice with significant anticancer effects [114]. Other modifications on PPI dendrimer surfaces, for enhancement in the accumulation of therapeutic nucleic acids in target cells, have also been made using the anti-CD44 antibody [115], maltose/anti-EGFRVIII single-chain antibody [116], folate [117], and luteinizing hormone-releasing peptide [94, 118]. Table 4 shows some examples of PPI dendrimers for gene delivery.
PLL dendrimers are a type of peptide dendrimer, whose core and branching units are composed mainly composed of lysines linked via peptide bonds [88, 120]. The surface lysine of PLL dendrimers has two primary amines that are frequently modified to allow transfection and the cytotoxic effect of nucleic acids [120]. The use of different amino acids as replacements for lysine residues can change the distribution and flexibility of charged groups, allowing additional interactions with nucleic acids. The addition of charged aliphatic amino acids, such as Arg, between inner Lys branching units, confers more charge and more hydrophilic character inside the dendrimer, increasing the affinity for DNA phosphate groups. For example, Gorzkiewicz et al. (2020) studied the formation of three types of G-3 PLL dendrimers with siRNA molecules; the G3 PLL dendrimers were modified, at the same points, with two lysine, histidine, or arginine residues between each pair of neighboring branching points of the standard PLL dendrimer. Such modifications changed binding stoichiometry and strength of dendrimer-siRNA interactions, electrostatic surface potential, and size, as well as cytotoxicity. For example, the low zeta potential of PLL dendrimers with His-His residues suggests a lower tendency to interact with the cell membrane and, thus, lower transfection efficiency, when compared to Lys-Lys or Arg-Arg modified dendriplexes [120]. Dendrigraft poly-L-lysine (DGL) polymers are a type of dendritic PLL derivative without tertiary amine groups, which have presented characteristics suitable for gene delivery (e.g., high density of amine groups on the surface) [121]. Li Ye et al. (2022) evaluated the potential of G2 y G5 DGL dendrimers for gene delivery. These dendriplexes were prepared with different siRNAs: fluorescein amidite (FAM)-siRNA, anti-polo-like kinase 1 (PLK1), siRNA (siPLK1), and anti-EGFR siRNA (siEGFR) for the evaluation of gene transfection, cellular uptake, endosomal escape of polyplexes, cytotoxicity and gene silencing efficacy in vitro, as well as treatment with polyplexes in vivo. These results provide an effective approach for improving the endosomal escape and transfection effectiveness of dendrimers.
Carbosilane dendrimer architecture includes silicon-carbon (Si-C), silicon-silicon (Si-Si), carbon-carbon triple (Si-C ≡ C-), and siloxane (Si-O) bonds. These bonds can be added to the surface or core of dendrimers [85, 122]. Carbosilane dendrimers are divided into two types: cationic and anionic dendrimers; there is evidence that cationic carbosilane dendrimers show high toxicity in comparison with anionic dendrimers. To decrease the cationic dendrimer cytotoxicity, surface modifications with negatively charged or neutral moieties and PEG modifications are recommended [82, 123, 124]. For example, to enhance the release of genetic material in target cells and reduce the cytotoxic effect, dendrimers with high water solubility, such as azide-terminated carbosilane dendrimers with two different propargyl amines, were applied [125]. Additionally, different degrees of PEGylation on cationic dendrimers loaded with miRNAs have shown to be successful, particularly in therapy against HIV/AIDS [82]. A study demonstrated that carbosilane and PAMAM dendrimers preserved anticancer siRNA cocktails better than phosphorous dendrimers [126]. Functionalization of cationic carbosilane dendrimers to nano-emulsions, through the carbodiimide reaction, favored the electrostatic attachment of antisense oligonucleotides to the surface of the nanoparticles, as well as the gene-silencing effect [127]. A nanosystem based on mesoporous silica nanoparticles, covered with carbosilane dendrimers, is an excellent transport of single-stranded oligonucleotides into the cells [128]. A nanosystem based on gold nanoparticles, conjugated to cationic carbosilane dendrimers (G1-G3) and loaded with siRNA, penetrated the target cells more efficiently with an increase in the generation of the dendrimers [129].
7 Dendrimers for Combined Therapies
The excellent capability of dendrimers to carry both individual molecules (drugs as antineoplastic agents, anti-inflammatory drugs, antibiotics, antibodies, genes, metal ions, metal nanoparticles, or radionuclides) and combined molecules, to a specific target, offers a broad spectrum to conventional therapy, radiotherapy, or combined therapy, with several medicinal and practical applications [130]. Specifically, in the anticancer medical research field, combined therapy has been reported in the use of carbosilane ruthenium dendrimers complexed with conventional anticancer drugs (methotrexate and doxorubicin), evaluated with human leukemic cells. The presence of ruthenium within the structure expands the anticancer properties of nanosystems containing antineoplastic compounds and reduces the viability of leukemia with regard to 1301 and HL-600 cancer cells [131].
On the other hand, G3 dendrimers bearing conjugated copper(II) on their surface have been reported to have antiproliferative activity related to their capacity to activate Bax translocation. The activity of multivalent Cu-conjugated dendrimers with different chemotherapeutic agents has been evaluated, showing an additive effect with taxanes, such as paclitaxel and the proteasome inhibitor MG132, and synergy with the topo II inhibitor doxorubicin [132].
Another application of combined therapy has been reported with the synthesis of multifunctional nanocarriers based on PAMAM dendrimers (G5), fixed to polydopamine (PDA)-coated magnetite nanoparticles (Fe3O4), allowing applied chemo- (doxorubicin) and photothermal therapy of liver cancer cells in vitro [133].
PAMAM-based dendrimers have been widely used to simultaneously carry both therapeutic molecules as radionuclides for dual therapy. G4 PAMAM dendrimers, modified in their surface with targeting ligands for the tumor microenvironment (e.g., bombesin, CXCR4, folate), have been radiolabeled with lutetium-177, a predilected radionuclide. These dendrimer structures combine radiotherapeutic effects with chemotherapy (paclitaxel), small molecules (C19), and metallic structures (gold nanoparticles), which produce a better cytotoxic effect in comparison with elements alone [8, 134, 135].
8 Radiolabeled Dendrimers as Theranostic Approaches
Dendrimers represent favorable choices as diagnostic, therapeutic, or theranostic probes. The variety in core materials and surface modification, as well as several targeting and radiolabeling strategies, have allowed dendrimers to be used as multifunctional platforms for multimodal imaging and therapeutics [27].
8.1 Radiolabeling
There are different strategies for radiolabeling, among them, the formation of complexes through chelating agents, the direct incorporation of radionuclides (via electrostatic interactions, adsorption or covalent bonds), or confinement strategies (trapping or encapsulation) [136]. The advantages and selection of these strategies will depend on the physiological environment and/or radiochemical parameters, such as radiolabeling efficacy, specific activity, and radiochemical purity. In general, they can be classified into direct and indirect radiolabeling techniques, which are described below [136, 137].
Indirect Radiolabeling
The selection of a bifunctional chelator agent (BFC) has the highest priority since the in vivo stability of the radiolabeling is highly dependent on the coordination chemistry between the radionuclide and the BFC. In indirect radiolabeling methods, a bifunctional chelating agent is used to conjugate dendrimers with a radionuclide through chemical linkers. A disadvantage of the addition of bifunctional groups to the dendrimer surface is that it can negatively affect its particle size, charge, and solubility [138]. The impact on the in vivo behavior is that it can cause dissociation of the radionuclide from the dendrimer, and this can result in erroneous image output and unwanted side effects [136]. Therefore, for indirect radiolabeling to be successful, the selection of a BFC with high in vivo stability is paramount.
BFCs consist of a metal-chelating unit and a reactive functionality; the former binds to metal radionuclides, and the latter is covalently conjugated to the surface of the dendrimers. Conjugation of BFCs with the dendrimer generally requires surface modification of the dendrimer. The chelator selection depends on the radionuclide chosen and the desired physicochemical properties [136, 139].
Figure 6 shows the structures of some chelators, such as diethylenetriaminepentaacetic acid (DTPA), 6-hydrazinonicotinyl, tetraazacyclododecanetetraacetic acid (DOTA), and 2,2′-(7-(2-((2,5-dioxopyrrolidin-1-yl)oxy)-2-oxoethyl)-1,4,7-triazonane-1,4-diyl)diacetic (NOTE) and derivatives that can be conjugated on the surface of PAMAM dendrimers to label with radionuclides such as 99mTc and 64Cu for SPECT and PET images, respectively. To label with other radionuclides such as iodine-131(131I), the phenol groups of 3-(4′-hydroxyphenyl)propionic acidOSu (HPAO) are employed to modify the surface of the PAMAM dendrimer and can be used for SPECT image-guided RT of tumors [140].
Chemical structure of some chelating agents used for the radiolabeling of PAMAM dendrimers
Direct Radiolabeling
One of the advantages of this technique is that in vivo dissociation of radiolabeled dendrimers can be minimized; however, some technical issues need to be addressed, such as radiation exposure of personnel during synthesis and reproducibility of radiolabeling. Surface modifications of radiolabeled dendrimers, using various polymer coatings, are commonly used to minimize interactions in vivo [136].
To prepare multifunctional dendrimers, the most common method is to covalently modify its surface and subsequently, several BFCs and different radionuclides can be attached to it. Some PAMAM structures have been radiolabeled through this technique, for example, 131I can be successfully attached to the surface of G5 PAMAM dendrimers prefunctionalized with HPAO (3-(4′-hydroxyphenyl) propionic acid-OSu) via phenol groups, using the chloramine T (tosylchloramide sodium) method [140]. Complexation of paramagnetic metal ions such as Mn(II) and Gd(III) has also been achieved through preconjugated chelators at the periphery of the dendrimer [141]; 99mTc or 64Cu radionuclides can also be linked to the dendrimer surface by chelation, for SPECT [142] or PET imaging applications [143]. To achieve dual-mode SPECT/MR imaging applications, Luo et al. placed Mn(II) and 99mTc onto the surface of G5 dendrimers via DOTA chelation [141].
Another radiolabeling technique used for dendrimers is interior trapping, in which the highly branched molecular structure of PAMAM dendrimers, with sufficient interior cavities to trap radiometallic NPs such as Au NPs, is exploited, exhibiting a superior X-ray attenuation property when compared to commercial iodinated contrast agents for CT.
8.2 Radionuclides
Depending on their medical applications, radionuclides can be classified as diagnostic or therapeutic. Diagnostic radionuclides used for SPECT imaging are gamma-emitters (energy range: 75–360 keV), while for PET imaging are positron-emitter radionuclides, which generate two 511 keV photons, via annihilation, for PET imaging [27]. Therefore, the selection of radionuclide depends on the intrinsic characteristics of each radionuclide. A variety of radionuclides, such as 67Ga, 123I, 131I, 111In, and 201TI, are suitable for SPECT imaging applications. In the case of 99mTc, it has been used for different applications, such as SPECT/optical, SPECT/MR, and SPECT/CT imaging (based on dendrimers) [27, 139] (Table 5).
9 Limitations of Dendrimers in Biomedical Applications
Liposomes, micelles, and dendrimers are cationic macromolecules with a positive charge on the surface, which tends to destabilize cell membranes and promote cell death [144]. The cytotoxicity of dendrimers relies on their charge, generation, and concentration. Positively charged products show increased toxicity compared to their negatively charged or neutral counterparts, while cytotoxicity increases with increasing generation and concentration [145]. The cytotoxicity of cationic dendrimers is due to the interaction between their positively charged dendrimer amines and negatively charged cell membrane compounds. This interaction promotes structural damage to the cell membrane via the formation of nanopores and the following leakage of cell content leading to cell death [12].
Another critical limitation of dendrimers for their biomedical application is their retention by the reticuloendothelial system. The administration of macromolecular anticancer drugs mainly depends on the permeable nature of the tumor’s vasculature, compared to the healthy vessels of normal organs. When administered intravenously, dendrimers tend to circulate for long periods, unless they are sufficiently small to be excreted by the kidney or stealthy enough to evade the phagocytic system of macrophages (reticuloendothelial system) [146]. Dendrimers can treat cancer because they can get trapped and accumulate in tumors. This EPR effect has explained the reason why macromolecules and nanoparticles are found in higher proportions in tumors than in healthy tissues. Although tumor accumulation is observed, cell uptake and intracellular release of encapsulated drugs in dendrimers have been questioned because PEG is employed for protecting dendrimers from the reticuloendothelial system uptake but prevents also the cell absorption and, as a consequence, the intracellular drug release [147]. Another limitation of dendrimer platforms is their use for the controlled release of drugs, due to the diversity of release mechanisms and the spectrum of release kinetics. For example, dendrimer-encapsulated drugs are quickly released, discharging their payload prematurely before the dendrimers reach a target location. In contrast, the release of drugs from functionalized dendrimers depends mainly on the bond character between the drug and the dendrimer periphery [148].
Nanoparticles as carriers of cancer drugs represent one of the fastest-growing areas of medical research and are considered one of the most favorable strategies to treat cancer. Liposomes and polymer conjugates were the first nanoparticles approved by the FDA. However, there are only five commercial formulations based on liposomes [149]. Due to the narrow emerging success in clinical translation, the FDA and the Nanotechnology Characterization Laboratory (NCL) stimulate a regulatory review of nanopharmaceuticals. The European Technology Platform on Nanomedicine created the European Nanocharacterization Laboratory in the framework of the Horizon 2020 project. Moreover, the FDA emitted the Industry Guide (“Pharmaceuticals, including biological products, containing nanomaterials”) to contribute providing legal certainty to this field [150].
10 Prospects for Clinical Translation
The goal of nanomedicine is to address specific clinical problems via the development of accurate diagnostic and therapeutic nanosystems. Several targeted and nontargeted nanosystems have emerged as strategies for delivering recombinant proteins, aptamers, therapeutic nucleic acid (siRNA, miRNA, or shRNA), and traditional cytotoxic drugs [14, 31, 84, 86, 107, 151, 152]. These nanosystems display excellent features such as high stability, biocompatibility, and efficient therapeutic effects, making them suitable as drug delivery scaffolds with high translational potential [14, 31]. Although many dendrimer formulations have been designed and evaluated over the years, there has been little done in clinical trials (Table 6) [14, 31, 84, 153]. Most of these nanosystems are based on fifth-generation PEGylated poly-lysine dendrimers conjugated with chemotherapeutic agents: docetaxel (DEP®-docetaxel), cabazitaxel (DEP®-cabazitaxel), or irinotecan (DEP®-irinotecan). For example, DEP®-docetaxel is found in phase II, in which the administration in patients with pancreatic, oesophageal, and gastric cancer has shown tumor reduction and prolonged stable disease, as well as notable lack of bone marrow toxicity and reduction of other common side effects (e.g., hair loss, mouth ulcers, anaphylaxis) [154]. DEP®-cabazitaxel is in Phase II with substantial tumor biomarker reductions (e.g., prostate-specific antigen) in prostate cancers [155]. In 2019, Starpharma in association with AstraZeneca announced that DEP®-Bcl2/xL started Phase 1 clinical trials. DEP®-Bcl2/xL is a dendrimer formulation conjugated to the AZD0466 inhibitor, which is a dual Bcl2 and Bcl/xL inhibitor, with excellent anticancer activity [156]. Another dendrimer in clinical trials is VivaGel®; it is a G4-PLL polyanionic dendrimer with 32 naphthalene disulfonate groups on its surface. It has potent topical vaginal microbicidal activity and is currently in Phase III, for the treatment of bacterial vaginosis (SPL7013 gel; astodrimer sodium) [153]. This same dendrimer showed a potent antiviral agent against the respiratory syncytial virus before and/or after exposure, using nasal spray technology [157]. Recently, the SPL7013 gel has also been shown to inactivate >99.9% of SARSCoV-2 within 1 min [157]. OP-101 is a G4 hydroxyl PAMAM dendrimer linked to N-acetyl cysteine (NAC) via a disulfide bond. NAC is released in the cell via cleavage of the disulfide bond by interaction with glutation [14, 158]. OP-101 is in Phase I of clinical trials. The safety, tolerability, and pharmacokinetics of OP-101 were evaluated after intravenous administration in healthy volunteers [158]. ImDendrim is an adendrimer in clinical trials composed of a 5G PLL dendrimer, combined with nitro imidazole-methyl-1,2,3-triazol-methyl-di-[2-pycolyl]amine and labeled with 188Rh [159]. 188Rh is beta emitter with a physical half-life of 16.9 h, Eβmax of 2.12 MeV, Eγ of 155 keV (15%), and mean tissue penetration of approximately11 mm; these properties make it suitable for theranostic applications [159, 160]. ImDendrim initiated a Phase I clinical trial in 2017, for the treatment of nonresponsive and inoperable liver cancers. Currently, there is no information concerning the status [161].
With regard to dendrimers that show potential to be used as prospects for clinical translation, there are targeted dendrimers for therapy and/or diagnosis. The advantage of these systems over nontargeted dendrimers is that solubility, bioavailability, and pharmacokinetic/pharmacodynamic (PK/PD) profile of the drugs (e.g., chemotherapeutic agents) can be improved. At the same time, these dendrimers can recognize specific sites on target cells, with high affinity, reducing side effects in healthy tissues. Low polydispersity and biocompatibility are two properties that must also be considered for the use of dendrimers in human trials. Several investigations highlight the in vitro and in vivo studies of dendrimers. Table 7 shows examples of prospects of dendrimers conjugated or complexed with targeting agents. An interesting study was performed by Huang et al. (2011), who developed a PEGylated PAMAM dendrimer conjugated to angiopep-2 (PAMAM-PEG-Angiopep) and complexed with DNA plasmid, to deliver tumor necrosis factor-related apoptosis-inducing ligands (TRAIL) to glioma cells and brain tumors. Angiopep-2 is a ligand for lipoprotein receptor-related protein 1 and TRAIL. It is a cytokine that activates apoptosis through binding to death receptors 4 (TRAILR1) and 5 (TRAIL-R2/KILLER). PAMAM-PEG-Angiopep/DNA, complexed with TRAIL DNA plasmid, displayed excellent blood-brain barrier penetration ability and a favorable biodistribution and pharmacodynamic profile in vivo, thus emerging as a promising dendrimer for targeted therapies [163]. Another prospect, as far as dendrimers go, is the PEG-cored PAMAM dendrimer conjugated to the Flt-1 antibody and loaded with gemcitabine; Flt-1 is a receptor for vascular endothelial growth factor (VEGF). This system has shown enhanced cytotoxicity of gemcitabine and increased the accumulation of the chemotherapeutic agent with satisfactory in vivo anticancer efficacy [151].
The G2-S16 water-soluble polyanionic carbosilane dendrimer (G2-S16 PCD) is another prospect for clinical translation. This is a polyanionic carbosilane dendrimer that has shown great potential as an antiviral agent to prevent HIV-1 sexual transmission, by blocking gp120/CD4/CCR5 interaction and providing a barrier against infection for long periods. The dendrimer has the capability to inhibit cell-to-cell HIV-1 transmission and is active against exposed mock and semen [164].
Dendrimers, in addition to being used for therapy, have been prepared as contrast agents for imaging techniques such as magnetic resonance, CT, and SPECT or PET [31]. In MRI, dendrimers have been used as carriers for the delivery of gadolinium ions. For example, biodistribution studies of PAMAM dendrimers conjugated to FA and dithylenetriamine pentaacetic acid (DTPA)-gadolinium have shown strong MRI signals in tumors, with negligible toxic effect [165].
11 Conclusion
Dendrimers have demonstrated their excellent capability to transport a broad variety of medically relevant molecules. For this reason, the current research focuses on modifying and improving dendrimeric structures to obtain new and innovative therapeutic alternatives in personalized medicine. Improved knowledge of the properties of dendrimers as drug- and gene-carrying macromolecules could lead, in the medium term, to clinical trials to introduce multifunctional drug delivery dendrimeric systems, leading to improved therapeutic efficacy over drugs alone. However, to a more considerable number of molecules in the functionalized dendrimers, there is a greater challenge to accurately assess their physicochemical and biological properties.
References
Chauhan A, Krynicka D, Singh MK. Therapeutic dendrimers. In: Chauhan A, Kulhari H, editors. Pharmaceutical applications of dendrimers. Elsevier; 2020. p. 275–87.
Bae YH, Park K. Targeted drug delivery to tumors: myths, reality and possibility. J Control Release. 2011;153(3):198–205.
Mittal P, Saharan A, Verma R, Altalbawy FMA, Alfaidi MA, Batiha GES, et al. Dendrimers: a new race of pharmaceutical nanocarriers. Biomed Res Int. 2021;2021:8844030.
Chaniotakis N, Thermos K, Kalomiraki M. Dendrimers as tunable vectors of drug delivery systems and biomedical and ocular applications. Int J Nanomedicine. 2015;11:1.
Postupalenko V, Einfalt T, Lomora M, Dinu IA, Palivan CG. Bionanoreactors: from confined reaction spaces to artificial organelles. In: Organic nanoreactors. Elsevier; 2016. p. 341–71.
Santos A, Veiga F, Figueiras A. Dendrimers as pharmaceutical excipients: synthesis, properties, toxicity and biomedical applications. Materials. 2020;13(1):65.
Kesharwani P, Amin MCIM, Giri N, Jain A, Gajbhiye V. Dendrimers in targeting and delivery of drugs. In: Nanotechnology-based approaches for targeting and delivery of drugs and genes. Elsevier; 2017. p. 363–88.
Gibbens-Bandala B, Morales-Avila E, Ferro-Flores G, Santos-Cuevas C, Luna-Gutiérrez M, Ramírez-Nava G, et al. Synthesis and evaluation of 177Lu-DOTA-DN(PTX)-BN for selective and concomitant radio and drug-therapeutic effect on breast cancer cells. Polymers (Basel). 2019;11(10):1572.
Wu LP, Ficker M, Christensen JB, Trohopoulos PN, Moghimi SM. Dendrimers in medicine: therapeutic concepts and pharmaceutical challenges. Bioconjug Chem. 2015;26(7):1198–211.
Sherje AP, Jadhav M, Dravyakar BR, Kadam D. Dendrimers: a versatile nanocarrier for drug delivery and targeting. Int J Pharm. 2018;548(1):707–20.
Kharwade R, More S, Warokar A, Agrawal P, Mahajan N. Starburst pamam dendrimers: synthetic approaches, surface modifications, and biomedical applications. Arab J Chem. Elsevier B.V. 2020;13:6009–39.
Janaszewska A, Lazniewska J, Trzepiński P, Marcinkowska M, Klajnert-Maculewicz B. Cytotoxicity of dendrimers. Biomolecules. 2019;9(8):330.
Fox LJ, Richardson RM, Briscoe WH. PAMAM dendrimer – cell membrane interactions. Adv Colloid Interface Sci. Elsevier B.V. 2018;257:1–18.
Dias AP, da Silva SS, da Silva JV, Parise-Filho R, Igne Ferreira E, Seoud O, et al. Dendrimers in the context of nanomedicine. Int J Pharm. Elsevier B.V. 2020;573:118814.
Mercer J, Helenius A. Gulping rather than sipping: macropinocytosis as a way of virus entry. Curr Opin Microbiol. 2012;15(4):490–9.
Zhang J, Liu D, Zhang M, Sun Y, Zhang X, Guan G, et al. The cellular uptake mechanism, intracellular transportation, and exocytosis of polyamidoamine dendrimers in multidrug-resistant breast cancer cells. Int J Nanomedicine. 2016;11:3677–90.
Manzanares D, Ceña V. Endocytosis: the nanoparticle and submicron nanocompounds gateway into the cell. Pharmaceutics. MDPI AG. 2020;12:371.
Foroozandeh P, Aziz AA. Insight into cellular uptake and intracellular trafficking of nanoparticles. Nanoscale Res Lett. 2018;13(1):339.
Kheraldine H, Rachid O, Habib AM, Al Moustafa AE, Benter IF, Akhtar S. Emerging innate biological properties of nano-drug delivery systems: a focus on PAMAM dendrimers and their clinical potential. Adv Drug Deliv Rev. Elsevier B.V. 2021;178:113908.
Forte M, Iachetta G, Tussellino M, Carotenuto R, Prisco M, de Falco M, et al. Polystyrene nanoparticles internalization in human gastric adenocarcinoma cells. Toxicol In Vitro. 2016;31:126–36.
Song Y, Shi Y, Zhang L, Hu H, Zhang C, Yin M, et al. Synthesis of CSK-DEX-PLGA nanoparticles for the oral delivery of exenatide to improve its mucus penetration and intestinal absorption. Mol Pharm. 2019;16(2):518–32.
Thakur NS, Patel G, Kushwah V, Jain S, Banerjee UC. Facile development of biodegradable polymer-based nanotheranostics: hydrophobic photosensitizers delivery, fluorescence imaging and photodynamic therapy. J Photochem Photobiol B Biol. 2019;193:39–50.
Seib FP, Jones AT, Duncan R. Comparison of the endocytic properties of linear and branched PEIs, and cationic PAMAM dendrimers in B16f10 melanoma cells. J Control Release. 2007;117(3):291–300.
Perumal OP, Inapagolla R, Kannan S, Kannan RM. The effect of surface functionality on cellular trafficking of dendrimers. Biomaterials. 2008;29(24–25):3469–76.
Kitchens KM, Foraker AB, Kolhatkar RB, Swaan PW, Ghandehari H. Endocytosis and interaction of poly (amidoamine) dendrimers with Caco-2 cells. Pharm Res. 2007;24(11):2138–45.
Li K, Wen S, Larson AC, Zhang Z, Chen Q, et al. Multifunctional dendrimer-based nanoparticles for in vivo MR/CT dual-modal molecular imaging of breast cancer. Int J Nanomed. 2013;8:2589.
Zhao L, Shi X, Zhao J. Dendrimer-based contrast agents for PET imaging. Drug Deliv. 2017;24(2):81–93.
Trujillo-Nolasco M, Morales-Avila E, Cruz-Nova P, Katti KV, Ocampo-García B. Nanoradiopharmaceuticals based on alpha emitters: recent developments for medical applications. Pharmaceutics. 2021;13(8):1123.
Zhao L, Zhu M, Li Y, Xing Y, Zhao J. Radiolabeled dendrimers for nuclear medicine applications. Molecules. 2017;22(9):1350.
Ma W, Fu F, Zhu J, Huang R, Zhu Y, Liu Z, et al. 64Cu-Labeled multifunctional dendrimers for targeted tumor PET imaging. Nanoscale. 2018;10(13):6113–6124.
Chis AA, Dobrea C, Morgovan C, Arseniu AM, Rus LL, Butuca A, et al. Applications and limitations of dendrimers in biomedicine. Molecules. 2020;25(17):3982.
Lim J, Guan B, Nham K, Hao G, Sun X, Simanek EE. Tumor uptake of triazine dendrimers decorated with four, sixteen, and sixty-four PSMA-targeted ligands: passive versus active tumor targeting. Biomol Ther. 2019;9(9):421.
Zhu J, Zhao L, Cheng Y, Xiong Z, Tang Y, Shen M, et al. Radionuclide 131 I-labeled multifunctional dendrimers for targeted SPECT imaging and radiotherapy of tumors. Nanoscale. 2015;7(43):18169–78.
Xing Y, Zhu J, Zhao L, Xiong Z, Li Y, Wu S, et al. SPECT/CT imaging of chemotherapy-induced tumor apoptosis using 99m Tc-labeled dendrimer-entrapped gold nanoparticles. Drug Deliv. 2018;25(1):1384–93.
Orocio-Rodríguez E, Ferro-Flores G, Santos-Cuevas CL, Ramírez FDM, Ocampo-García BE, Azorín-Vega E, et al. Two novel nanosized radiolabeled analogues of somatostatin for neuroendocrine tumor imaging. J Nanosci Nanotechnol. 2015;15(6):4159–69.
Zhang P, Ma X, Guo R, Ye Z, Fu H, Fu N, et al. Organic nanoplatforms for iodinated contrast media in CT imaging. Molecules. 2021;26(23):7063.
Avila-Salas F, González RI, Ríos PL, Araya-Durán I, Camarada MB. Effect of the generation of PAMAM dendrimers on the stabilization of gold nanoparticles. J Chem Inf Model. 2020;60(6):2966–76.
Li D, Wen S, Shi X. Dendrimer-entrapped metal colloids as imaging agents. Wiley Interdiscip Rev Nanomed Nanobiotechnol. 2015;7(5):678–90.
Xiao Y, Shi X. Improved tumor imaging using dendrimer-based nanoplatforms. Nanomedicine. 2019;14(19):2515–8.
Liu R, Guo H, Ouyang Z, Fan Y, Cao X, Xia J, et al. Multifunctional core–shell tecto dendrimers incorporated with gold nanoparticles for targeted dual mode CT/MR imaging of tumors. ACS Appl Bio Mater. 2021;4(2):1803–12.
Chandra S, Nigam S, Bahadur D. Combining unique properties of dendrimers and magnetic nanoparticles towards cancer theranostics. J Biomed Nanotechnol. 2014;10(1):32–49.
Barrett T, Ravizzini G, Choyke P, Kobayashi H. Dendrimers in medical nanotechnology. IEEE Eng Med Biol Mag. 2009;28(1):12–22.
Luo K, Liu G, She W, Wang Q, Wang G, He B, et al. Gadolinium-labeled peptide dendrimers with controlled structures as potential magnetic resonance imaging contrast agents. Biomaterials. 2011;32(31):7951–60.
Liu Y, Zhang N. Gadolinium loaded nanoparticles in theranostic magnetic resonance imaging. Biomaterials. 2012;33(21):5363–75.
Fahmy TM, Fong PM, Goyal A, Saltzman WM. Targeted for drug delivery. Mater Today. 2005;8(8):18–26.
Barraza LF, Jiménez VA, Alderete JB. Effect of PEGylation on the structure and drug loading capacity of PAMAM-G4 dendrimers: a molecular modeling approach on the complexation of 5-fluorouracil with native and PEGylated PAMAM-G4. Macromol Chem Phys. 2015;216(16):1689–701.
Mahmoudi A, Jaafari MR, Ramezanian N, Gholami L, Malaekeh-Nikouei B. BR2 and CyLoP1 enhance in-vivo SN38 delivery using pegylated PAMAM dendrimers. Int J Pharm. 2019;564:77–89.
Carvalho MR, Carvalho CR, Maia FR, Caballero D, Kundu SC, Reis RL, et al. Peptide-modified dendrimer nanoparticles for targeted therapy of colorectal cancer. Adv Ther. 2019;2(11):1900132.
Kianamiri S, Dinari A, Sadeghizadeh M, Rezaei M, Daraei B, Bahsoun NEH, et al. Mitochondria-targeted polyamidoamine dendrimer–curcumin construct for hepatocellular cancer treatment. Mol Pharm. 2020;17(12):4483–98.
Kaur A, Jain K, Mehra NK, Jain NK. Development and characterization of surface engineered PPI dendrimers for targeted drug delivery. Artif Cells Nanomed Biotechnol. 2017;45(3):414–25.
Wang Y, Cao X, Guo R, Shen M, Zhang M, Zhu M, et al. Targeted delivery of doxorubicin into cancer cells using a folic acid–dendrimer conjugate. Polym Chem. 2011;2(8):1754.
Karimi S, Namazi H. A photoluminescent folic acid-derived carbon dot functionalized magnetic dendrimer as a pH-responsive carrier for targeted doxorubicin delivery. New J Chem. 2021;45(14):6397–405.
Chanphai P, Thomas TJ, Tajmir-Riahi HA. Application and biomolecular study of functionalized folic acid-dendrimer nanoparticles in drug delivery. J Biomol Struct Dyn. 2021;39(3):787–94.
Narmani A, Mohammadnejad J, Yavari K. Synthesis and evaluation of polyethylene glycol- and folic acid-conjugated polyamidoamine G4 dendrimer as nanocarrier. J Drug Deliv Sci Technol. 2019;50:278–86.
Singh P, Gupta U, Asthana A, Jain NK. Folate and folate−PEG−PAMAM dendrimers: synthesis, characterization, and targeted anticancer drug delivery potential in tumor bearing mice. Bioconjug Chem. 2008;19(11):2239–52.
Narmani A, Arani MAA, Mohammadnejad J, Vaziri AZ, Solymani S, Yavari K, et al. Breast tumor targeting with PAMAM-PEG-5FU-99mTc as a new therapeutic nanocomplex: in in-vitro and in-vivo studies. Biomed Microdevices. 2020;22(2):31.
Barraza LF, Jiménez VA, Alderete JB. Methotrexate complexation with native and PEGylated PAMAM-G4: effect of the PEGylation degree on the drug loading capacity and release kinetics. Macromol Chem Phys. 2016;217(4):605–13.
Liu C, Gao H, Zhao Z, Rostami I, Wang C, Zhu L, et al. Improved tumor targeting and penetration by a dual-functional poly(amidoamine) dendrimer for the therapy of triple-negative breast cancer. J Mater Chem B. 2019;7(23):3724–36.
Zhu F, Xu L, Li X, Li Z, Wang J, Chen H, et al. Co-delivery of gefitinib and hematoporphyrin by aptamer-modified fluorinated dendrimer for hypoxia alleviation and enhanced synergistic chemo-photodynamic therapy of NSCLC. Eur J Pharm Sci. 2021;167:106004.
He X, Alves CS, Oliveira N, Rodrigues J, Zhu J, Bányai I, et al. RGD peptide-modified multifunctional dendrimer platform for drug encapsulation and targeted inhibition of cancer cells. Colloids Surf B: Biointerfaces. 2015;125:82–9.
Sheikh A, Md S, Kesharwani P. RGD engineered dendrimer nanotherapeutic as an emerging targeted approach in cancer therapy. J Control Release. 2021;340:221–42.
Lu Y, Han S, Zheng H, Ma R, Ping Y, Zou J, et al. A novel RGDyC/PEG co-modified PAMAM dendrimer-loaded arsenic trioxide of glioma targeting delivery system. Int J Nanomedicine. 2018;13:5937–52.
Anbazhagan R, Muthusamy G, Krishnamoorthi R, Kumaresan S, Rajendra Prasad N, Lai J, et al. PAMAM G4.5 dendrimers for targeted delivery of ferulic acid and paclitaxel to overcome P-glycoprotein-mediated multidrug resistance. Biotechnol Bioeng. 2021;118(3):1213–23.
Vats K, Sharma R, Sharma AK, Sarma HD, Satpati D. Assessment of 177 Lu-labeled carboxyl-terminated polyamidoamine (PAMAM) dendrimer-RGD peptide conjugate. J Pept Sci. 2022;28(2):e3366.
Yuan A, Yang B, Wu J, Hu Y, Ming X. Dendritic nanoconjugates of photosensitizer for targeted photodynamic therapy. Acta Biomater. 2015;21:63–73.
Nour S, Bolandi B, Imani R. In: Razavi M, editor. Chapter 4 – Nanotechnology in gene therapy for musculoskeletal regeneration. Academic Press; 2020. p. 105–36.
Goswami R, Subramanian G, Silayeva L, Newkirk I, Doctor D, Chawla K, et al. Gene therapy leaves a vicious cycle. Front Oncol. 2019;9:297.
Papanikolaou E, Bosio A. The promise and the hope of gene therapy. Front Genome Ed. 2021;3:4.
Raguraman P, Balachandran AA, Chen S, Diermeier SD, Veedu RN. Antisense oligonucleotide-mediated splice switching: potential therapeutic approach for cancer mitigation. Cancers (Basel). 2021;13(21):5555.
Montaño-Samaniego M, Bravo-Estupiñan DM, Méndez-Guerrero O, Alarcón-Hernández E, Ibáñez-Hernández M. Strategies for targeting gene therapy in cancer cells with tumor-specific promoters. Front Oncol. 2020;10:605380.
Di Fusco D, Dinallo V, Marafini I, Figliuzzi MM, Romano B, Monteleone G. Antisense oligonucleotide: basic concepts and therapeutic application in inflammatory bowel disease. Front Pharmacol. 2019;10:305.
Rinaldi C, Wood MJA. Antisense oligonucleotides: the next frontier for treatment of neurological disorders. Nat Rev Neurol. 2018;14(1):9–21.
Lenz G. The RNA interference revolution. Braz J Med Biol Res. 2005;38(12):1749–57.
Hu B, Zhong L, Weng Y, Peng L, Huang Y, Zhao Y, et al. Therapeutic siRNA: state of the art. Signal Transduct Target Ther. 2020;5(1):101.
O’Brien J, Hayder H, Zayed Y, Peng C. Overview of microRNA biogenesis, mechanisms of actions, and circulation. Front Endocrinol. 2018;9:402.
Lambeth LS, Smith CA. Short hairpin RNA-mediated gene silencing. In: Methods in molecular biology (Clifton, NJ); 2013. p. 205–32.
Nelson NG, Skeie JM, Muradov H, Rowell HA, Seo S, Mahajan VB. CAPN5 gene silencing by short hairpin RNA interference. BMC Res Notes. 2014;7:642.
Moore CB, Guthrie EH, Huang MTH, Taxman DJ. Short hairpin RNA (shRNA): design, delivery, and assessment of gene knockdown. Methods Mol Biol. 2010;629:141–58.
Wu H, Chaudhary AK, Mahato RI. Gene therapy. In: Crommelin DJA, Sindelar RD, Meibohm B, editors. Pharmaceutical biotechnology. Cham: Springer International Publishing; 2019. p. 323–55.
Nour S, Bolandi B, Imani R. Nanotechnology in gene therapy for musculoskeletal regeneration. In: Razavi M, editor. Nanoengineering in musculoskeletal regeneration. Elsevier; 2020. p. 105–36.
Kulkarni JA, Witzigmann D, Thomson SB, Chen S, Leavitt BR, Cullis PR, et al. The current landscape of nucleic acid therapeutics. Nat Nanotechnol. 2021;16(6):630–43.
Royo-Rubio E, Rodríguez-Izquierdo I, Moreno-Domene M, Lozano-Cruz T, de la Mata FJ, Gómez R, et al. Promising PEGylated cationic dendrimers for delivery of miRNAs as a possible therapy against HIV-1 infection. J Nanobiotechnol. 2021;19(1):158.
Hersh J, Condor Capcha JM, Iansen Irion C, Lambert G, Noguera M, Singh M, et al. Peptide-functionalized dendrimer nanocarriers for targeted microdystrophin gene delivery. Pharmaceutics. 2021;13(12):2159.
Surekha B, Kommana NS, Dubey SK, Kumar AVP, Shukla R, Kesharwani P. PAMAM dendrimer as a talented multifunctional biomimetic nanocarrier for cancer diagnosis and therapy. Colloids Surf B: Biointerfaces. 2021;204:111837.
Rabiee N, Ahmadvand S, Ahmadi S, Fatahi Y, Dinarvand R, Bagherzadeh M, et al. Carbosilane dendrimers: drug and gene delivery applications. J Drug Deliv Sci Technol. 2020;59:101879.
Wang Y, Ye M, Xie R, Gong S. Enhancing the in vitro and in vivo stabilities of polymeric nucleic acid delivery nanosystems. Bioconjug Chem. 2019;30(2):325–37.
Dzmitruk V, Apartsin E, Ihnatsyeu-Kachan A, Abashkin V, Shcharbin D, Bryszewska M. Dendrimers show promise for siRNA and microRNA therapeutics. Pharmaceutics. 2018;10(3):126.
Palmerston Mendes L, Pan J, Torchilin V. Dendrimers as nanocarriers for nucleic acid and drug delivery in cancer therapy. Molecules. 2017;22(9):1401.
Fant K, Esbjörner EK, Jenkins A, Grossel MC, Lincoln P, Nordén B. Effects of PEGylation and acetylation of PAMAM dendrimers on DNA binding, cytotoxicity and in vitro transfection efficiency. Mol Pharm. 2010;7(5):1734–46.
Pedziwiatr-Werbicka E, Ferenc M, Zaborski M, Gabara B, Klajnert B, Bryszewska M. Characterization of complexes formed by polypropylene imine dendrimers and anti-HIV oligonucleotides. Colloids Surf B: Biointerfaces. 2011;83(2):360–6.
Froehlich E, Mandeville JS, Kreplak L, Tajmir-Riahi HA. Aggregation and particle formation of tRNA by dendrimers. Biomacromolecules. 2011;12(7):2780–7.
Cao Y, Liu X, Peng L. Molecular engineering of dendrimer nanovectors for siRNA delivery and gene silencing. Front Chem Sci Eng. 2017;11(4):663–75.
Dehshahri A, Sadeghpour H. Surface decorations of poly(amidoamine) dendrimer by various pendant moieties for improved delivery of nucleic acid materials. Colloids Surf B: Biointerfaces. 2015;132:85–102.
Noske S, Karimov M, Aigner A, Ewe A. Tyrosine-modification of polypropylenimine (PPI) and polyethylenimine (PEI) strongly improves efficacy of siRNA-mediated gene knockdown. Nano. 2020;10(9):1809.
Taratula O, Garbuzenko OB, Kirkpatrick P, Pandya I, Savla R, Pozharov VP, et al. Surface-engineered targeted PPI dendrimer for efficient intracellular and intratumoral siRNA delivery. J Control Release. 2009;140(3):284–93.
Luong D, Kesharwani P, Deshmukh R, Mohd Amin MCI, Gupta U, Greish K, et al. PEGylated PAMAM dendrimers: enhancing efficacy and mitigating toxicity for effective anticancer drug and gene delivery. Acta Biomater. 2016;43:14–29.
Shakhbazau A, Isayenka I, Kartel N, Goncharova N, Seviaryn I, Kosmacheva S, et al. Transfection efficiencies of PAMAM dendrimers correlate inversely with their hydrophobicity. Int J Pharm. 2010;383(1–2):228–35.
Froehlich E, Mandeville JS, Weinert CM, Kreplak L, Tajmir-Riahi HA. Bundling and aggregation of DNA by cationic dendrimers. Biomacromolecules. 2011;12(2):511–7.
Soltani F, Ramezani M, Amel Farzad S, Mokhtarzadeh A, Hashemi M. Comparison study of the effect of alkyl-modified and unmodified PAMAM and PPI dendrimers on solubility and antitumor activity of crocetin. Artif Cells Nanomed Biotechnol. 2017;45(7):1356–62.
Khan OF, Zaia EW, Jhunjhunwala S, Xue W, Cai W, Yun DS, et al. Dendrimer-inspired nanomaterials for the in vivo delivery of siRNA to lung vasculature. Nano Lett. 2015;15(5):3008–16.
Liu J, Gu C, Cabigas EB, Pendergrass KD, Brown ME, Luo Y, et al. Functionalized dendrimer-based delivery of angiotensin type 1 receptor siRNA for preserving cardiac function following infarction. Biomaterials. 2013;34(14):3729–36.
Arima H, Tsutsumi T, Yoshimatsu A, Ikeda H, Motoyama K, Higashi T, et al. Inhibitory effect of siRNA complexes with polyamidoamine dendrimer/α-cyclodextrin conjugate (generation 3, G3) on endogenous gene expression. Eur J Pharm Sci. 2011;44(3):375–84.
Liu X, Liu C, Catapano CV, Peng L, Zhou J, Rocchi P. Structurally flexible triethanolamine-core poly(amidoamine) dendrimers as effective nanovectors to deliver RNAi-based therapeutics. Biotechnol Adv. 2014;32(4):844–52.
Shen X, Corey DR. Chemistry, mechanism and clinical status of antisense oligonucleotides and duplex RNAs. Nucleic Acids Res. 2018;46(4):1584–600.
Dung TH, Kim JS, Juliano RL, Yoo H. Preparation and evaluation of cholesteryl PAMAM dendrimers as nano delivery agents for antisense oligonucleotides. Colloids Surf A Physicochem Eng Asp. 2008;313–314:273–7.
Yoo H, Juliano RL. Enhanced delivery of antisense oligonucleotides with fluorophore-conjugated PAMAM dendrimers. Nucleic Acids Res. 2000;28(21):4225–31.
Kang H, DeLong R, Fisher MH, Juliano RL. Tat-conjugated PAMAM dendrimers as delivery agents for antisense and siRNA oligonucleotides. Pharm Res. 2005;22(12):2099–106.
Kang C, Yuan X, Li F, Pu P, Yu S, Shen C, et al. Evaluation of folate-PAMAM for the delivery of antisense oligonucleotides to rat C6 glioma cells in vitro and in vivo. J Biomed Mater Res A. 2010;93(2):585–94.
Nourazarian AR, Pashaei-Asl R, Omidi Y, Najar AG. c-Src antisense complexed with PAMAM denderimes decreases of c-Src expression and EGFR-dependent downstream genes in the human HT-29 colon cancer cell line. Asian Pac J Cancer Prev. 2012;13(5):2235–40.
Nourazarian AR, Najar AG, Farajnia S, Khosroushahi AY, Pashaei-Asl R, Omidi Y. Combined EGFR and c-Src antisense oligodeoxynucleotides encapsulated with PAMAM Denderimers inhibit HT-29 colon cancer cell proliferation. Asian Pac J Cancer Prev. 2012;13(9):4751–6.
Márquez-Miranda V, Peñaloza JP, Araya-Durán I, Reyes R, Vidaurre S, Romero V, et al. Effect of terminal groups of dendrimers in the complexation with antisense oligonucleotides and cell uptake. Nanoscale Res Lett. 2016;11(1):66.
Hashemi M, Parhiz H, Mokhtarzadeh A, Tabatabai SM, Farzad SA, Shirvan HR, et al. Preparation of effective and safe gene carriers by grafting alkyl chains to generation 5 polypropyleneimine. AAPS PharmSciTech. 2015;16(5):1002–12.
Hollins AJ, Benboubetra M, Omidi Y, Zinselmeyer BH, Schatzlein AG, Uchegbu IF, et al. Evaluation of generation 2 and 3 poly(propylenimine) dendrimers for the potential cellular delivery of antisense oligonucleotides targeting the epidermal growth factor receptor. Pharm Res. 2004;21(3):458–66.
Jugel W, Aigner A, Michen S, Hagstotz A, Ewe A, Appelhans D, et al. Targeted RNAi of BIRC5/survivin using antibody-conjugated poly(propylene imine)-based polyplexes inhibits growth of PSCA-positive tumors. Pharmaceutics. 2021;13(5):676.
Gu J, Fang X, Hao J, Sha X. Reversal of P-glycoprotein-mediated multidrug resistance by CD44 antibody-targeted nanocomplexes for short hairpin RNA-encoding plasmid DNA delivery. Biomaterials. 2015;45:99–114.
Tietze S, Schau I, Michen S, Ennen F, Janke A, Schackert G, et al. A poly(propyleneimine) dendrimer-based polyplex-system for single-chain antibody-mediated targeted delivery and cellular uptake of SiRNA. Small. 2017;13(27):1700072.
Sideratou Z, Kontoyianni C, Drossopoulou GI, Paleos CM. Synthesis of a folate functionalized PEGylated poly(propylene imine) dendrimer as prospective targeted drug delivery system. Bioorg Med Chem Lett. 2010;20(22):6513–7.
Taratula O, Garbuzenko O, Savla R, Wang YA, He H, Minko T. Multifunctional nanomedicine platform for cancer specific delivery of siRNA by superparamagnetic iron oxide nanoparticles-dendrimer complexes. Curr Drug Deliv. 2011;8(1):59–69.
Shah V, Taratula O, Garbuzenko OB, Taratula OR, Rodriguez-Rodriguez L, Minko T. Targeted nanomedicine for suppression of CD44 and simultaneous cell death induction in ovarian cancer: an optimal delivery of siRNA and anticancer drug. Clin Cancer Res. 2013;19(22):6193–204.
Gorzkiewicz M, Kopec OK, Janaszewska A, Konopka M, Zbieta P, Edziwiatr-Werbicka E, Tarasenko II, et al. Poly(lysine) dendrimers form complexes with siRNA and provide its efficient uptake by myeloid cells: model studies for therapeutic nucleic acid delivery. Int J Mol Sci. 2020;21:3138.
Ye L, Liu H, Fei X, Ma D, He X, Tang Q, et al. Enhanced endosomal escape of dendrigraft poly-L-lysine polymers for the efficient gene therapy of breast cancer. Nano Res. 2022;15(2):1135–44.
Kim C, Hong J. Carbosilane and carbosiloxane dendrimers. Molecules. 2009;14(9):3719–30.
Sánchez-Nieves J, Fransen P, Pulido D, Lorente R, Muñoz-Fernández MÁ, Albericio F, et al. Amphiphilic cationic carbosilane–PEG dendrimers: synthesis and applications in gene therapy. Eur J Med Chem. 2014;76:43–52.
Krasheninina OA, Apartsin EK, Fuentes E, Szulc A, Ionov M, Venyaminova AG, et al. Complexes of pro-apoptotic siRNAs and carbosilane dendrimers: formation and effect on cancer cells. Pharmaceutics. 2019;11(1):25.
Arnáiz E, Doucede LI, García-Gallego S, Urbiola K, Gómez R, Tros de Ilarduya C, et al. Synthesis of cationic carbosilane dendrimers via click chemistry and their use as effective carriers for DNA transfection into cancerous cells. Mol Pharm. 2012;9(3):433–47.
Ionov M, Lazniewska J, Dzmitruk V, Halets I, Loznikova S, Novopashina D, et al. Anticancer siRNA cocktails as a novel tool to treat cancer cells. Part (A). Mechanisms of interaction. Int J Pharm. 2015;485(1–2):261–9.
Fornaguera C, Grijalvo S, Galán M, Fuentes-Paniagua E, de la Mata FJ, Gómez R, et al. Novel non-viral gene delivery systems composed of carbosilane dendron functionalized nanoparticles prepared from nano-emulsions as non-viral carriers for antisense oligonucleotides. Int J Pharm. 2015;478(1):113–23.
Martínez Á, Fuentes-Paniagua E, Baeza A, Sánchez-Nieves J, Cicuéndez M, Gómez R, et al. Mesoporous silica nanoparticles decorated with carbosilane dendrons as new non-viral oligonucleotide delivery carriers. Chem Eur J. 2015;21(44):15651–66.
Abashkin V, Pędziwiatr-Werbicka E, Gómez R, de la Mata FJ, Dzmitruk V, Shcharbin D, et al. Prospects of cationic carbosilane dendronized gold nanoparticles as non-viral vectors for delivery of anticancer siRNAs siBCL-xL and siMCL-1. Pharmaceutics. 2021;13(10):1549.
Tekade RK, Dutta T, Gajbhiye V, Jain NK. Exploring dendrimer towards dual drug delivery: pH responsive simultaneous drug-release kinetics. J Microencapsul. 2009;26(4):287–96.
Michlewska S, Maroto M, Hołota M, Kubczak M, Sanz del Olmo N, Ortega P, et al. Combined therapy of ruthenium dendrimers and anti-cancer drugs against human leukemic cells. Dalton Trans. 2021;50(27):9500–11.
Mignani S, el Brahmi N, Cresteil T, Majoral JP. First-in-class combination therapy of a copper(II) metallo-phosphorus dendrimer with cytotoxic agents. Oncology (Switzerland). 2018;94(5):324–8.
Jędrzak A, Grześkowiak BF, Coy E, Wojnarowicz J, Szutkowski K, Jurga S, et al. Dendrimer based theranostic nanostructures for combined chemo- and photothermal therapy of liver cancer cells in vitro. Colloids Surf B: Biointerfaces. 2019;173:698–708.
Trujillo-Nolasco M, Cruz-Nova P, Ferro-Flores G, Gibbens-Bandala B, Morales-Avila E, Aranda-Lara L, et al. Development of 177 Lu-DN(C19)-CXCR4 ligand nanosystem for combinatorial therapy in pancreatic cancer. J Biomed Nanotechnol. 2021;17(2):263–78.
Mendoza-Nava H, Ferro-Flores G, Ramírez FDM, Ocampo-García B, Santos-Cuevas C, Aranda-Lara L, et al. 177Lu-dendrimer conjugated to folate and bombesin with gold nanoparticles in the dendritic cavity: a potential theranostic radiopharmaceutical. J Nanomater. 2016;2016:1–11.
Ranjbar Bahadori S, Mulgaonkar A, Hart R, Wu C, Zhang D, Pillai A, et al. Radiolabeling strategies and pharmacokinetic studies for metal based nanotheranostics. Wiley Interdiscip Rev Nanomed Nanobiotechnol. 2021;13:e1671.
Brechbiel MW. Bifunctional chelates for metal nuclides. Q J Nucl Med Mol Imaging. 2008;52(2):166–73.
Enrique MA, Mariana OR, Mirshojaei SF, Ahmadi A. Multifunctional radiolabeled nanoparticles: strategies and novel classification of radiopharmaceuticals for cancer treatment. J Drug Target. 2015;23(3):191–201.
Aranda-Lara L, García BEO, Isaac-Olivé K, Ferro-Flores G, Meléndez-Alafort L, Morales-Avila E. Drug delivery systems-based dendrimers and polymer micelles for nuclear diagnosis and therapy. Macromol Biosci. 2021;21(3):2000362.
Xiao T, Li D, Shi X, Shen M. PAMAM Dendrimer-based nanodevices for nuclear medicine applications. Macromol Biosci. 2020;20(2):1900282.
Luo Y, Zhao L, Li X, Yang J, Guo L, Zhang G, Shen M, Zhao J, Shi X. The design of a multifunctional dendrimer-based nanoplatform for targeted dual mode SPECT/MR imaging of tumors. J Mater Chem B. 2016;4:7220–7225.
Criscione JM, Dobrucki LW, Zhuang ZW, Papademetris X, Simons M, Sinusas AJ, et al. Development and application of a multimodal contrast agent for SPECT/CT hybrid imaging. Bioconjug Chem. 2011;22(9):1784–92.
Li ZB, Cai W, Cao Q, Chen K, Wu Z, He L, et al. 64Cu-labeled tetrameric and octameric RGD peptides for small-animal PET of tumor αvβ3 integrin expression. J Nucl Med. 2007;48(7):1162–71.
SVENSON S, TOMALIA D. Dendrimers in biomedical applications—reflections on the field. Adv Drug Deliv Rev. 2005;57(15):2106–29.
Araújo R, Santos S, Igne Ferreira E, Giarolla J. New advances in general biomedical applications of PAMAM dendrimers. Molecules. 2018;23(11):2849.
Kobayashi H, Turkbey B, Watanabe R, Choyke PL. Cancer drug delivery: considerations in the rational design of nanosized bioconjugates. Bioconjug Chem. 2014;25(12):2093–100.
Wang M, Thanou M. Targeting nanoparticles to cancer. Pharmacol Res. 2010;62(2):90–9.
Wolinsky J, Grinstaff M. Therapeutic and diagnostic applications of dendrimers for cancer treatment. Adv Drug Deliv Rev. 2008;60(9):1037–55.
Saha AK, Zhen MYS, Erogbogbo F, Ramasubramanian AK. Design considerations and assays for hemocompatibility of FDA-approved nanoparticles. Semin Thromb Hemost. 2020;46(05):637–52.
Franiak-Pietryga I, Ziemba B, Messmer B, Skowronska-Krawczyk D. Dendrimers as drug nanocarriers: the future of gene therapy and targeted therapies in cancer. In: Dendrimers – fundamentals and applications. InTech; 2018.
Öztürk K, Esendağlı G, Gürbüz MU, Tülü M, Çalış S. Effective targeting of gemcitabine to pancreatic cancer through PEG-cored Flt-1 antibody-conjugated dendrimers. Int J Pharm. 2017;517(1):157–67.
Lee IH, An S, Yu MK, Kwon HK, Im SH, Jon S. Targeted chemoimmunotherapy using drug-loaded aptamer–dendrimer bioconjugates. J Control Release. 2011;155(3):435–41.
Mignani S, Shi X, Rodrigues J, Roy R, Muñoz-Fernández Á, Ceña V, et al. Dendrimers toward translational nanotherapeutics: concise key step analysis. Bioconjug Chem. 2020;31(9):2060–71.
Starpharma-DEP®-Docetaxel. Starpharma commences phase 2 DEP® docetaxel trial-starpharma. 2022. Available online: https://starpharma.com/drug_delivery/dep_docetaxel. Accessed on 10 Feb 2022.
Starpharma-DEP®Cabazitaxel. Starpharma to commence DEP®cabazitaxel phase 1/2 trial—starpharma. 2022. Available online: https://starpharma.com/drug_delivery/dep_cabazitaxel. Accessed on 10 Feb 2022.
Starpharma-Partnered-DEP® Products. Partnered-DEP® products – AZD0466_Starpharma. 2022. Available online: https://starpharma.com/drug_delivery/dep-azd0466. Accessed on 10 Feb 2022.
Mignani S, Shi X, Guidolin K, Zheng G, Karpus A, Majoral JP. Clinical diagonal translation of nanoparticles: case studies in dendrimer nanomedicine. J Control Release. 2021;337:356–70.
ClinicalTrials.gov. A study to evaluate the safety, tolerability, and pharmacokinetics of OP-101 after intravenous administration in healthy volunteer. 2022. Available online: https://clinicaltrials.gov/ct2/show/NCT03500627?term=dendrimer. Accessed on 12 Feb 2022.
Yang G, Sadeg N, Tahar HB. New potential in situ anticancer agent derived from [188Re]rhenium nitro-imidazole ligand loaded 5th generation poly-L-lysine dendrimer for treatment of transplanted human liver carcinoma in nude mice. Drug Des Open Access. 2017;06(01):1–7.
Lepareur N, Lacœuille F, Bouvry C, Hindré F, Garcion E, Chérel M, et al. Rhenium-188 labeled radiopharmaceuticals: current clinical applications in oncology and promising perspectives. Front Med. 2019;6:132.
ClinicalTrials.gov. Treatment of non-responding to conventional therapy inoperable liver cancers by in situ introduction of ImDendrim (ImDendrim). Study NCT03255343 [Internet]. 2017. Available from: https://clinicaltrials.gov/ct2/history/NCT03255343?V_1=View.
Starpharma-DEP® Irinotecan. Starpharma commences phase 2 DEP® irinotecan trial-starpharma. 2022. Available online: https://starpharma.com/drug_delivery/dep_irinotecan. Accessed on 10 Feb 2022.
Huang S, Li J, Han L, Liu S, Ma H, Huang R, et al. Dual targeting effect of Angiopep-2-modified, DNA-loaded nanoparticles for glioma. Biomaterials. 2011;32(28):6832–8.
Relaño-Rodríguez I, Muñoz-Fernández MÁ. Emergence of nanotechnology to fight HIV sexual transmission: the trip of G2-S16 polyanionic carbosilane dendrimer to possible pre-clinical trials. Int J Mol Sci. 2020;21(24):9403.
Cheng Z, Thorek DLJ, Tsourkas A. Gadolinium-conjugated dendrimer nanoclusters as a tumor-targeted T1 magnetic resonance imaging contrast agent. Angew Chem Int Ed. 2010;49(2):346–50.
Taghdisi SM, Danesh NM, Ramezani M, Lavaee P, Jalalian SH, Robati RY, et al. Double targeting and aptamer-assisted controlled release delivery of epirubicin to cancer cells by aptamers-based dendrimer in vitro and in vivo. Eur J Pharm Biopharm. 2016;102:152–8.
Lin L, Fan Y, Gao F, Jin L, Li D, Sun W, et al. UTMD-promoted co-delivery of gemcitabine and miR-21 inhibitor by dendrimer-entrapped gold nanoparticles for pancreatic cancer therapy. Theranostics. 2018;8(7):1923–39.
Long Z, Wu YP, Gao HY, Li YF, He RR, Liu M. Functionalization of halloysite nanotubes via grafting of dendrimer for efficient intracellular delivery of siRNA. Bioconjug Chem. 2018;29(8):2606–18.
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The authors acknowledge the Mexican National Council of Science and Technology for the CONACYT-CB-A1S38087 and CF-2019-263379 Grants.
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Gibbens-Bandala, B., Trujillo-Nolasco, M., Cruz-Nova, P., Aranda-Lara, L., Ocampo-García, B. (2022). Dendrimers as Targeted Systems for Selective Gene and Drug Delivery. In: Barabadi, H., Mostafavi, E., Saravanan, M. (eds) Pharmaceutical Nanobiotechnology for Targeted Therapy. Nanotechnology in the Life Sciences. Springer, Cham. https://doi.org/10.1007/978-3-031-12658-1_13
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